Fig. 10.

Steady-state Ca²⁺ profiles in a hair cell stereocilium predicted from a three-dimensional diffusion model. A, Vertical section through the center of a cylindrical stereocilium, diameter 0.4 μm, with a Ca²⁺ source, the transducer channels, placed at the distal tip. Pseudocolor images of the Ca²⁺concentration profiles are shown for three different intracellular BAPTA concentrations. The Ca²⁺ entry was calculated from experimental data of the standing transducer current and the channel permeability in 0.07 mm external Ca²⁺. Note the Ca²⁺ gradient is steepest for the highest buffer concentration. B, Ca²⁺ profiles down the axis of the cylindrical stereocilium, length 6 μm, for the three BAPTA concentrations in 2.8 mm external Ca²⁺ (top) and 0.07 mm external Ca²⁺(bottom). Note that the curves for the different buffers cross at a distance of 20–40 nm from the source.